The present invention relates to filters and, more particularly, to a microwave integrated circuit including a bandpass filter.
In microwave communications, microwave integrated circuit (MIC) filters are used to select utilized frequencies and to reject unwanted frequencies which can result in noise. One design goal of such filters is to obtain sharp out-of-band rejection.
One commonly employed microwave wave circuit (MIC) bandpass filter is the combline filter. This filter includes a longitudinally extending transmission line section and plural, usually four, spaced resonators extending from and orthogonal to the transmission line. The four resonator combline filter represents an useful compromise between economy and effectiveness. More effective filtering can be achieved using more than four resonators, but the added cost and complexity of manufacture tend to outweigh the gain in effectiveness. Furthermore, the added bulk of the larger filters is a significant disadvantage in space and other applications where size and weight are at a premium. What is needed is a compact and economical filter which provides greater filtering effectiveness than the available four-section filter.